A widely used optical instrument to investigate the composition of the atmosphere is the LIDAR which corresponds to the abbreviation of LIght Detection And Ranging. The molecules, aerosols, water and the ice particles present in the atmosphere scatter and attenuate the light in different intensities depending on the type and the concentration of each one of these components. Considering this principle, a lidar use a laser beam to provides profiles of atmospheric parameters such as aerosol backscatter, humidity, temperature, ozone concentration, cloud phase and wind speed, amount others.
Fig. 1. Working principle of a lidar system.
Basically, the Lidar system consists in the transmission of short laser pulses (of green light at 532 nm of wavelength in this case) from the ground level to the upper atmosphere. Part of the laser pulse is attenuated and backscattered by the clouds, gases and aerosols present in the atmosphere at each height level and collected by a telescope (see fig. 1). The light is filtered in order to reduce the background signal from the sunlight and after that is analyzed by a detection system. The return time of the backscattered light allows to determine its altitude and build a vertical profile along the atmospheric path. Finally the information of the signal is stored in a computer.
During the current mission, we are going to deploy a new Lidar designed by the EPFL-LTE team and let it collecting information during all the year. One of the main objectives using this instrument is to discriminate between liquid drops and non-spherical ice crystals present in the atmosphere.